Light-sensitive photographic materials generally comprise a support and coated on one or both sides hydrophilic colloid layers including a light-sensitive silver halide emulsion layer (or layers) and, if desired or necessary, other non light-sensitive layers such as subbing layers, intermediate layers, protective layers, backing layers, antihalation layers and the like. Examples of supports include films of a polyalpha-olefin (such as polyethylene, polystyrene, etc.), a polyester (such as polyethyleneterephthalate, etc.), a cellulose ester (such as cellulose triacetate, etc.), paper, synthetic paper or resin-coated paper and the like.
Since the support of a light-sensitive photographic material has electrical insulating properties, static charges are frequently generated during production and use of said photographic material due to contact friction and separation between surfaces of the same kind of materials or surfaces of different kinds of materials. The accumulated static charges may cause various problems. For example, the accumulated static charges may discharge before development of the photographic material and generate light to which the silver halides are sensitive; after development of the photographic material, dot-like marks (called positive static marks) and branch-like marks (called negative static marks) are formed. Said static marks negatively affect the photographic images, particularly X-ray materials for medical and industrial use where static marks may lead to a dangerous misreading. Additionally, the accumulated static charges may attract dust or other particles on the surface of the support negatively affecting the quality during the coating step.
Static charges are, in general, related to the surface resistivity and charge level. Therefore, the accumulation of static charges can be prevented by reducing the surface resistivity or by lowering the charge level.
The surface resistivity of a layer is reduced by addition to the layer of substances which increase the electrical conductivity and release the accumulated electrical charges in a very short time before discharge. In the art, various processes have been disclosed for improving the electrical conductivity of supports and surface layers of photographic materials, and many hygroscopic substances, water soluble inorganic salts, surface active agents, polymers and the like have been suggested to such purpose. For example, polymers as described in U.S. Pat. Nos. 2,822,157, 2,861,056, 2,972,535, 3,062,785, 3,169,949, 3,260,706, 3,262,807, 3,514,291, 3,589,908, 3,607,286, 3,615,531, etc., surface active agents as described in GB patents 861,134, 1,285,647, 1,259,398, 1,330,356, etc., in U.S. Pat. Nos. 2,982,651, 3,428,456, 3,457,076, 3,454,652, 3,552,972, 3,589,906, 3,640,748, 3,655,387, etc., nitrates, metal oxides, semiconductors, colloidal silica or colloidal alumina, etc., as described in GB patent 2,075,208, in U.S. Pat. Nos. 3,062,700, 3,254,833, 3,525,621, 4,264,707, etc., have been proposed for this purpose. Among said substances, non-ionic surfactants having polyoxyethylene chains have been described as having excellent antistatic properties.
Another method to prevent accumulation of static charges is that of lowering the charge level by controlling the triboelectric charge generated on the surface of photographic materials to reduce generation caused by friction and separation of surfaces, as described for example in U.S. Pat. No. 3,888,678. According to this method, fluorine containing compounds, surface active agents, polymers, etc. have been disclosed as substances to reduce static charges. Particularly, fluorine containing surface active agents have been described, for the above purposes, for example in the above mentioned US patent, in GB patents 1,330,356 and 1,524,631, in GB patent application 2,096,782, in U.S. Pat. Nos. 3,666,478, 3,589,906, 3,884,699 and 4,330,618, in JA patent 26687/77 and in JA patent applications 46733/74 and 32322/76.
However, for preventing the accumulation of electric charges, it is difficult to select a single antistatic agent owing to the different kinds of supports, coating compositions and surfaces of materials which are to be considered. Therefore, methods have been described for improving the characteristics of static chargeability of photographic materials, such as those described for example in U.S. Pat. No. 3,884,699 (use of a fluorinated cationic or anionic surfactant in combination with a non-fluorinated betaine surfactant and/or a N-oxide surfactant), GB patent 1,496,534 (use of organic fluorinated compounds in combination with carboxy group-containing organic compounds), U.S. Pat. No. 4,013,696 (use of cationic fluorinated alkyl surfactants in combination with non-ionic alkylphenoxypolypropyleneoxide surfactants), U.S. Pat. No. 4,367,283 (use of non-ionic surfactants having a polyoxyethylene group in combination with anionic surfactants and fluorinated anionic surfactants) and U.S. Pat. No. 4,596,766 (use of a non-ionic surfactant having a polyoxyethylene group in combination with a fluorinated organic compound in a surface layer having a specific amount of said fluorinated compound).
In spite of the numerous methods and compounds described for increasing electrical conductivity and lowering charge level, the production of photographic materials exhibiting a reduced static chargeability is very difficult. Problems are encountered with insufficient reduction in surface resistivity at low humidities, with the contact between the surfaces of the photographic material itself or between such material and other material surfaces at high temperatures and humidities. Such problems become more severe as the sensitivity of the photographic material is higher and the processing speed is increased (such as when the photographic material is used in rapid processing machines where the film is conveyed at a high speed by means of rollers or other surfaces which exert thereon a strong pressure and friction action). On the other hand, compounds which have good antistatic properties, cannot often be used because they negatively affect the photographic properties (such as sensitivity, fog, contrast), image quality (such as graininess, sharpness), the performance of processing chemistries where said antistatic compounds may accumulate, the coating quality, etc., or lose their antistatic ability over a period of time during storage of the photographic material.
Accordingly, the application of antistatic compounds to light-sensitive photographic materials is very difficult and there is a continuous need for providing improved antistatic compositions which do not adversely affect the other characteristics of the material.